DE2160907A1 - Retroreflective elements and retroreflective assemblies comprising these elements - Google Patents

Description

Priority: lA. December! 97o, No. 97660, USA

The invention relates to retroreflective elements and Retroreflective arrangements with such elements, in particular retroreflective arrangements, the spherical lens elements contain.

A common embodiment of a retroreflective assembly includes small spherical lens elements, for example small glass microspheres or beads, and either a diffuse or specularly reflective material adjacent on their back. The refractive indices of the materials are selected and the respective components are arranged in a known manner so as to obtain maximum retroreflective efficiency receives. To create a track arrangement, such microspheres are expediently hemispherical in one suitable binder embedded, the reflective material is contained in the binder. Different types of specular, reflective material have been used,

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including metal flakes, for example aluminum flakes or chips. It is still possible, specularly reflective Material directly on the microsphere surface to deposit a hemisphere. A particularly brownable specular reflective material is obtained by vapor deposition of metal, e.g. aluminum, to a hemispherical portion of a glass microsphere (U.S. Patent No. 2,963,378). Unfortunately metallic specular reflectors have several serious disadvantages, one of which is common light absorption. Additionally some metals, such as aluminum, are subject to corrosion. Furthermore, the color of the one is Retroreflective arrangement of reflected light, the one metallic mirror reflector used, not easily adjustable, a glossy white is difficult to achieve, especially when using aluminum. Color effects are generally limited by the particular color characteristics of the specular reflective material available, except when the paint is incorporated into the glass spheres or contained in a top coating over the glass spheres.

The aim of the invention is therefore to provide retroreflective elements and to provide retroreflective assemblies whose specular reflectors are improved against damage as a result Less sensitive to corrosion, which can be used to regulate the color or create new visual effects and whose reflection is improved for white light.

An example embodiment of the invention is explained in more detail with the aid of the accompanying drawing.

1 and 2 show schematically in section two embodiments of retroreflective arrangements according to the invention.

The retroreflective arrangement according to the invention has lens elements in the form of microspheres with a diameter of Io up to 2oo u,

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preferably 25 to 75 ρ diameter. Adjacent to the microspheres is a material for the mirror reflection, a dielectric mirror being used as such a material. This material comprises a transparent layer with a refractive index η., The surfaces of the layer being in contact with substances which have the refractive indices η _η or n ». n _o and η are at least 0.1, preferably 0.3 »larger or smaller than n ₁ . At least the substance that is in contact with the surface that is closest to the spherical lens element is transparent or translucent. The transparent layer has an optical thickness that corresponds to the odd multiple, ie _1, 3, 7 ... So either _no > n. < _No or _no <η.> N ^. The fabrics on each side

fci X J Ct X Jf

the transparent layer can have either both a refractive index have that is greater or less than the refractive index

τα. is. If n. Is greater than both n _o and η, then n. Χ X c * j X lies

preferably in the range from 1.7 to Λ, 9 and _no and n "before-

* 3 preferably in the range between 1.2 and 1.7 · If conversely n _{1 is} smaller than both n »and η, n .. is preferably in a range between 1.2 and 1.7« while n _o and n_ are preferably between 1.7 and 4.9. The mirror reflector thus obtained comprises substances which are arranged in contact with one another, at least one of which is in the form of a layer. The arrangement has an alternating sequence of refractive indices. With the exception of the material furthest from the ball lens, all fabrics are necessarily transparent. In a preferred embodiment, the arrangement consists of two to seven layers, preferably three to five layers, adjacent to the ball lens element. All translucent materials should be clear or free of inclusions or essentially colorless in order to reduce light absorption to a minimum and light reflection

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to bring it to a maximum value. In doing so, however, a large variety of visual effects should be achieved if desired can ^ if one or more fabrics are colored.

The retroreflective arrangement shown in FIG. 1 comprises small spherical lens elements 1 with a refractive index n ", a transparent layer 2 thereon with the refractive index H ₁ , a binding agent 3 for the spherical lens elements, which has the refractive index n_ and a suitable base k. As shown, the transparent layer 2 can be applied hemispherically to the spherical lens element or can be layered over the entire spherical surface of the lens element. In the latter case, the layer, if its refractive index is smaller than that of the lens element, can also serve as an anti-reflective layer on that part of the surface of the spherical lens element which is not embedded in the binder. If the binder 3 and the backing or support layer k are transparent, all light which passes through the transparent layer 2 can penetrate the entire arrangement so that it can be seen on the rear side of the arrangement. Therefore, another surface can be attached, glued, or adjoined thereto from which the light can be reflected back through the assembly. If, for example, such a web sits on a surface with a wood grain, the effect of the grain can be seen through the layer structure, which is useful when decorative effects are desired in addition to the retroreflective properties.

The retroreflective arrangement shown in FIG. 2 uses ale 'mirror reflector multiple layers with successively alternating indices of refraction. A spherical lens element 5 is coated with transparent layers 6 and 7 with the refractive index n _o and n _{4, respectively.} The binder 8 on the web 9 ice base has a refractive index n_. If more than two transparent layers are provided, the retroreflective efficiency is increased and the amount of transmitted light,

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■ reduced accordingly. The light that comes through the Multi-layer mirror reflector is allowed to pass through of course any filler, pigment, colorant, metal flake and the like in the binder or in the Underlay is diffusely reflected, creating a special visual Effects are achieved.

The application of alternating layers of dielectric materials with high and low refractive index for creation the reflection through phase ex-a mood or equality or increase or increase in the reflected light multiple interfaces is required for optical instrumentation, such as dispersion filters, interference filters, dichroic Mirrors and thin film polarization filters (Scientific American, Volume 223, Mr. 6, December 197o, pp 59 to 75) Man. but has never considered to apply this technique for retroreflective assemblies, in particular then when mirror reflection matorialien in connection used with very small spherical lens elements will. Indeed, the optical interference filament theory is based on flat surfaces. Although it is known is that the theory can also be applied to surfaces with relatively large radii of curvature, for example on Radii of curvature in the range above 2.5 mm says this Known theory not previously that the increase or strengthening of the reflection at much smaller radii of curvature takes effect. In fact, through the predicted intensity distribution images, which is divided by the WeIJ.en front division in concentrically curved surfaces with small radii of curvature can be expected to be the desired Magnification of the mirror reflection. would be destroyed or at least greatly reduced.

Among the many water-insoluble compounds that act as translucent substances within the area with the

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desired refractive index can be used, are substances with a high refractive index, such as CdS, CeO, CsI, GaAs, Ge, InAs, InP, InSb, ZrO ₀ , Bi ₀ O ₀ , ZnSe, ZnS, Wo_, PbS, PbSe, PbTe, RbI , Si, Ta ₃ O, Te, TiO ₃₁ substances with a low refractive index, such as Al ₂ O ₃ , AlF ₃₁ CaF ₂ , CeF ₃ , LiF, MgF ₃₁ Na g ThOF, SiOp, elastomeric copolymers of perfluoropropylene and vinylidene fluoride with a refractive index von VL, 38 usii .. If the insolubility in water is not important, other substances, for example NaCl, can also be used

™ become. Further substances are in "Thin Film Phenomena" by K.L. Chopra, page 75o, McGraw-Hill Book Company, New York, 1969. You can use the ball lens elements in an expedient manner arranged or formed after the lens elements are temporarily substantially hemispherical are embedded in a plastic covered heated sheet, for example in polyethylene covered paper. The coating is carried out by vapor deposition on the exposed lens surfaces in one or more stages to the desired number of layers to create in an alternating sequence of refractive indices. When the specular reflector is at a specified distance from the

If the surface of the ball lens element is to be arranged, a transparent layer or layer can first be applied to the lens element surface in order to create the gap (US Pat. No. 2,4o7,680).

Another advantage of the retroreflective elements according to the invention relies on the ability to create a dielectric mirror structure on the glass microsphere that is selective only reflects part of the light in the visible spectrum (e.g. a dielectric narrow dispersion filter), whereby the visible light is in the pass band width transmitted and the visible light is reflected outside the transmission range. Such dielectric mirror assemblies are of the type found in the literature for

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the use as a dispersion filter or band filter are known. Such a known dielectric mirror structure with reflective properties in only a part of the visible spectrum is described in the reference "Scientific American, Optical Interference Coatings" by Phillip Baumeister and Geraldpincus, pages 59 to 75% December 197o. Here, z \ te ± quarter-wavelength stacks, each of which has layers with alternating indices of refraction (i.e. two dielectric mirrors) and which both preferably have the same number of quarter-wavelength layers and a significant transmission component, are separated by a spacer layer, the optical of which Strength is equal to a quarter wavelength of the light to be let through. With such a structure on the microspheres according to the invention, it is possible to create retroreflective microspheres which have an adjusted color retroreflection and accordingly a limited and colored permeability component. For example, if a glass microsphere is provided with two spaced apart dielectric mirrors as described above, which has a transmittance that is narrowly responsive to the green part of the visible spectrum, the retroreflective component will include the remainder of the visible spectrum, i.e. red and blue or magenta . The green light transmitted through the retroreflective microspheres can be used to aid vision through diffuse reflection.

In contrast to aluminum, the mirror reflectors according to the invention do not necessarily absorb considerable amounts of the incident light, although a fraction of the light is usually transmitted. As mentioned above, the greater the number of alternating fabrics or layers, the higher the reflection of light and the lower the transmission of light. You can use ko to 50 alternating layers, five to seven layers are

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however, sufficient to produce a reflection efficiency of 9o to 98 % . The fact that a smaller number of layers produces a lower reflection and proportionally a higher light transmission can lead to the advantage that when the transmitted light comes into contact with a diffuse reflection material, for example with a fluorescent substance or with a color pigment, in the Base or the microsphere binding agent, an improved diffuse reflection can be achieved if the retroreflective microspheres are contained in a web material that is designed to be seen in normal lighting as well as in retroreflection.

The invention is further developed in the following by means of examples explained.

example 1

A sheet of paper coated on one side with low density polyethylene is covered on the polyethylene side with a monolayer of glass spheres having a refractive index of 1.93 and a diameter between k5 and 70µ. These spheres are embedded in the polyethylene to a depth of approximately 30 to ko% of their diameter by heating the web to 138 ° C. The side of the track with the exposed spherical sides is vacuum coated with Na AlF, whose refractive index is between 1.35 and 1.39, to form a first layer and then vacuum with BX2O with a refractive index of about 1.92 to form a second layer steamed. The two layers have an optical strength of about a quarter of a wavelength, the strength being 55oo A * The coated ones. Beads are blended with a slurry (0.25 mm wet thickness)

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_ Q -

fluorescent pigment (37 t5% by weight) and an alkyd resin binder (30.6% by weight) in 2o, 8% by weight xylene and 3.1% by weight Butanol coated. The coating is cured for five minutes at 66 ° C and twelve minutes at 93 ° C. On the A white pigmented adhesive layer is applied to the fluorescent layer, containing 7/9 parts by weight of titanium dioxide and 3 »^ parts of a thermoplastic, highly crystalline polyurethane resin, 1Λ, 6 parts of a dioctyl phthalate plasticizer and 21.8 parts of a vinyl chloride-vinyl acetate copolymer (87% by weight or 13% by weight) in 18.7 parts of toluene and 25.7 parts of methyl ethyl ketone and 7i2 parts of dimethylformamide, the Stax * - ke of the wet coating is 0.15 «nni. After the three Drying at 66 ° C. for ten minutes and drying at 93 ° C. for ten minutes, the web becomes one Pressure of 2.1 lcp / cin and a temperature of 99 C on one with Hot-laminated adhesive-coated cotton cloth, the adhesive being a plasticized vinyl chloride-vinyl acetate copolymer (87% by weight and 13% by weight). Finally will stripped the polyethylene-coated paper from the beads, thereby exposing the surfaces of the beads. The product produced is highly fluorescent

2 has a retroreflective intensity of 135 cd / m / lux and has retained the properties that it feels like cotton cloth feels and is just as easy to grip.

Example 2

Ee an arrangement is made with the exception is identical to the arrangement of Example 1, that the Bi "O ~. Step is omitted. The completed arrangement has

an unusual fluorescent appearance and a retroion intensity of 24,
as much as white color.

2
reflection intensity of 24.5 cd / m / lux, so approximately

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- Io -

Example 3

An arrangement is made which is identical to the arrangement of Example 1 with the exception that the slurry applied directly to Bi O as a layer contains TxO _o white pigment (7.9 parts by weight) instead of a fluorescent pigment, and that the binder is a mixture from Io, 3 parts of a thermoplastic, highly crystalline polyurethane resin and 7.9 parts of a vinyl chloride-vinyl acetate copolymer (86 % by weight vinyl chloride, 13% by weight of vinyl acetate, 1 % dibasic acid) in 29.6 parts of methyl ethyl ketone and 351 parts of dimethylformamide is. The fabric produced is a white, permanent, drapable retroreflective sheeting with a retroreflective intensity

of 139 cd / m / lux.

To determine dex retroreflective intensity, the the following experimental procedures were used. A light projector with a maximum lens diameter of 2.5 cm, which can project a uniform light, is used to illuminate the Sample used. The light falling on the sample has a color temperature of 285 K. That reflected from the test surface Light is measured with a photoelectric receiver, its responsiveness to color sensitivity corresponds to the average human eye set to daylight. The dimensions of the active area on the Receiver is dimensioned so that no point on the circumference is now more than 12.7 away from the center. On one level The samples become black test areas of approximately 0.8 μm attached. The samples are located 1Λ.25 m from the projector lens and removed from the recipient. The area of the sample is

2
carries, o, o929 m. The light intensity of the probe hitting the test area and the light intensity hitting the receiver as a result of the reflection from the test area

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measured at 5 angles of incidence and 0.2 divergence angles. the Reflection intensity in cd / m "/ lux is obtained from the following equation calculated:

_{R =} Er (d ² )

It (A)

where R is the retroreflective intensity, Er is the luminosity impinging on the receiver, Es is the luminosity impinging on a plane that is perpendicular to the incident beam g at the sample position, measured in the same units as Er, d is the distance in m from the sample to .. ; Projector and

■ 2 A is the area of the test surface in m.

These retroreflective intensities represent the effect of a Light beam, which in a retroreflective glass ball enters and exits in such a way that any surface or interfacial effects are doubled. The above procedure is as . Retroreflective intensity test in the "United States Federal Specification" No. L-S-300A (Jan. 7 197ο).

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Claims (1)

A η s ρ r ü c h. d f 1. ) Retroreflective arrangement, characterized by spherical lens elements from Io to 2oo u in diameter and mirror reflectors adjacent to the lens elements, which are dielectric mirrors. 2. Retroreflective arrangement according to claim I _1, characterized in that the mirror reflectors have a transparent layer with the refractive index n. The surfaces of this layer are in contact with substances with the refractive index n _o and η, both n _o and η to at least each o, l is greater or less than n. that at least the substance which is in contact with the surface which is closest to the spherical lens element is transparent, and that this transparent layer has an optical strength which is an odd multiple of about a quarter wavelength of light in the wavelength range of about 3800 until corresponds to A loooo. 3. retroreflective arrangement according to claim 1 or 2, characterized in that the mirror reflectors comprise a plurality of transparent layers which successively alternately have refractive indices of at least o, i difference. k, retroreflective arrangement according to claim 1 or 2, characterized in that the successively alternating refractive indices have a difference of at least 0.3. 209827/0906 5. retroreflective arrangement according to claim 3 or 4, characterized marked, dtiß the multitude of transparent. Layers two to seven layers adjacent to the sphere lins enelemonte. " 6. Retroreflective arrangement according to one of the preceding claims, characterized in that the material with the refractive index n _{o is} the material of the spherical lens elements. 7 «retroreflective arrangement according to one of the preceding Claims, characterized in that the material with the refractive index n "is a binder for the lens elements is. 8. retroreflective arrangement according to one of claims 1 to 6, characterized in that the material with the refractive index n "is a second transparent layer, which has an optical strength which corresponds to that of the other transparent layer. 9. retroreflective arrangement according to one of the preceding claims, characterized in that τι. between 1.7 and 4.9 and n _o and n_ each between 1.2 and 1.7. 10. retroreflective arrangement according to one of claims 1 to 8, characterized in that n. Between 1.2 and 1.7 and n _o and n_ are each between 1.7 and 4.9. 11. Retroreflective arrangement according to one of the preceding Claims, characterized in that the ball lens elements and the adjoining mirror reflectors are partially embedded in a binder which is a Contains diffuse reflective material. 2 0 9 8 2 7/0906 ° ^{HmHAl IN} SPECTED 12. Retroreflective microspheres for retroreflective assemblies according to one of the preceding claims, characterized in that the balls have a diameter between Io and 2oo u and a dielectric Have mirrors on / exnem part of the microsphere surface. 13 · retroreflective microspheres according to claim 12, characterized in that they have a refractive index n _o and I ^ on a semicircular part of the surface at least two transparent layers with an optical thickness that corresponds to an odd multiple of about a quarter wavelength of the light in the wavelength range of about 38 ° with 10000 A, the transparent layer being the microsphere is closest, has a refractive index of n ₁ and the next adjacent transparent layer has a refractive index of η, and η is at least 0.1 greater or less than both _no and _no . 209827/0906